The Ghosts were agents of H.I.V.E., who acted as the terrorist group's grunt soldier forces, security guards, and representatives.
H.I.V.E. operatives were nicknamed "Ghosts" by the media of Star City, and later Team Arrow, who faced the difficulty of targeting the movements of the terrorist organization, since its agents being uncooperative and had a tendency to kill themselves (usually with special poisonous capsules hidden in their mouths), rather than allow to be tortured. H.I.V.E. agents would quickly disappear after a successful mission, never revealing the secrets of their leadership, and their own identities were kept secret, if not erased from any database, thus becoming metaphorical "ghosts" of people long thought dead or non-existent, like Andy Diggle.
The Ghosts use modern weaponry and high-tech equipment. Their operators wear bulletproof vests and use advanced firearms and grenades. Their unique uniforms are adorned with a pattern of hexagons, resembling a honeycomb of a beehive, painted on a gray-colored fabric.
H.I.V.E. started using these operatives long before the confrontation with Oliver Queen. For example, in 1975, Damien Darhk and two of his Ghosts went to a weapons sale held by Vandal Savage in Norway, planning to buy a nuclear warhead from him. H.I.V.E. put in an initial bid of $100 million but were outbid by Martin Stein, which led to a confrontation between two men. Stein's associate Mick Rory started to get angry with Damien and then threatened him, forcing Savage to intervene. As a fight ensued, Damien and the Ghosts left the premises of the Norwegian military storage facility. 
In 1987, the Ghosts were present at the White House basement during a deal between Damien Darhk and the KGB. The opportunistic KGB agents intended to exchange a priceless artifact for the United States (Earth-One)' nuclear codes, while Darhk also left a bomb to kill Ronald Reagan and Mikhail Gorbachev, along with everybody in the White House. When the Legends showed up to stop Darhk, the KGB suspected treason on H.I.V.E.'s behalf, with Damien deciding that the deal is done and order the Ghosts to kill all of KGB agents present.
After Floyd Lawton was incarcerated for threatening the lives of his family, Mina Fayad approached him as a representative of H.I.V.E., and offered Lawton money to assassinate Andrew Diggle, though - unknown to Lawton - Diggle survived the attempt as H.I.V.E. had secretly replaced Lawton's bullets with non-lethal rounds. Diggle himself ended up becoming an agent of H.I.V.E., serving as one of its Ghosts.
Terrors of Star City
After Ra's al Ghul's failed attempt to destroy Star City and Damien Darhk, H.I.V.E. soldiers began attacking the city in waves, receiving their nickname of "Ghosts". The Ghosts brought Alvarez to Damien Darhk for execution and later assisted him in the attempt to blow up Star City's central train station.
To ensure the security of the identities of his Ghosts, Darhk sent Quentin Lance on a mission to erase their names from governmental databases. Lance went through with the operation but managed to convince Darhk to tell him about Andrew Diggle, whose name had been on the list of Ghosts given to him.
A division of Ghosts guarded the imprisoned Ray Palmer. Team Arrow managed to successfully rescue Ray, although Oliver barely escaped being strangled to death by chains under control of Darhk's magic.
Fighting the Green Arrow
Green Arrow and his team continued to plague H.I.V.E.'s operations in Star City culminating in a surgical strike against the HQ of the Ghosts by the Green Arrow and his team in an effort to rescue Andrew Diggle, who the team had found out was alive. The Ghosts fought Team Arrow but were overpowered and the team escaped with Diggle. H.I.V.E. later raided an A.R.G.U.S. facility to steal a chemical bomb, only to be confronted by Team Arrow, who disarmed the Ghosts of their guns with a magnetic arrow. The Ghosts fought the team but before an outcome could be revealed, The Flash whisked the Team away to deal with problems in Central City.
In an act of revenge Darhk personally led a squad of Ghosts to attack Oliver's Holiday Party, and took John Diggle, Felicity Smoak, and Thea Queen. However, Laurel Lance and Malcolm Merlyn interfered and saved Oliver's compatriots. Darhk immediately left the scene, sending his partners to a safe location, and fought with Merlyn while the rest of Team Arrow fought Darhk's Ghosts, resulting in Damien's near death when Merlyn blew up their hideout. The surviving Damien Darhk sent Ghosts to kill Queen. They attacked Oliver's limousine, firing upon him and Felicity and leaving Oliver injured and Felicity unresponsive.
After his son, William Clayton, was kidnapped by Damien Darhk and Malcolm Merlyn, the Green Arrow hunted down the Ghosts mercilessly, trying to force them to give him information on Darhk's location, to no avail.
A group of Ghosts, along with Malcolm Merlyn's supporters from the former League of Assassins, had assaulted a weapon truck, only to be interrupted by Green Arrow, Spartan, and Andy Diggle. However, the attack was a ruse, needed to cover up Malcolm Merlyn's attack on the Arrowcave.
Andy Diggle and the other Ghosts accompanied Damien Darhk after he freed himself from imprisonment and, in a bid for power, eliminated other high-ranked H.I.V.E. members, seizing the control of organization for himself. The Ghosts were also sent to guard H.I.V.E.'s underground facility "Tevat Noah", which was a part of the Genesis project. They made sure Thea Queen wouldn't escape said facility after she ended up there with her boyfriend Alex Davis.
The Ghosts acted as guards for the Tevat Noah facility – the "home in the new era" that H.I.V.E. created for its members. They also served as security for H.I.V.E. leaders like Malcolm Merlyn, who tried to persuade Thea Queen that staying in the facility was in her best interests. However, even the Ghosts' unbreakable ability to protect the organization's secrets was proven moot before the wrath of Lonnie Machin, who has hunted down and tortured many Ghosts to find the location of Damien Darhk. Infiltrating the facility, Machin has stunned a Ghost and sought to sabotage Telvat Noah's life support systems.
Danny Brickwell and Michael Amar also led a group of Ghosts to hunt down Noah Kuttler, the Calculator, who was considered to be the only person capable of hacking A.R.G.U.S.'s Rubicon protocol. The Ghosts were unsuccessful as Kuttler himself gunned down some of his pursuers, while Oliver Queen and John Diggle handled the rest. After the Calculator and his daughter, Felicity Smoak, came close to shutting down the Rubicon protocol, the Ghosts attacked their location once again but were repelled by A.R.G.U.S. forces. 
Two Ghosts accompanied Malcolm Merlyn when he was hunting for Lonnie Machin. At Merlyn's orders, they took hold of the distraught Thea Queen, placing her under guard, and later fought off Green Arrow and Spartan who tried to save her. They also stood guard at H.I.V.E. headquarters, as Damien Darhk and Ruvé Adams discussed their plans to take the Rubicon protocol back from Team Arrow with the help of Cooper Seldon.
The Ghosts accompanied Damien Darhk during his visit to Felicity Smoak's apartment when he threatened Donna Smoak. Green Arrow and Spartan intervened and had to fight off the Ghosts, only to see Darhk escape. They later assaulted the Arrowcave and assisted Darhk during his final showdown against Oliver Queen and the people of Star City.
Ghosts appeared among other foes from Team Arrow's past during the dream-like shared hallucination imposed by the Dominators on Oliver Queen, Sara Lance, John Diggle, Thea Queen and Ray Palmer. These foes were conjured by the Dominators to keep the captured humans from breaking away from the hallucination.
DC's Legends of Tomorrow
Behind the scenes
- In DC Comics, the Ghost is an enemy of Captain Atom. Curiously, on "Arrow" and "DC's Legends of Tomorrow", the Ghosts are recurring antagonists of the Atom.
- Although H.I.V.E. minions in DC Comics weren't referred to as "Ghosts", they are quite often noticeable thanks to the hexagonal pattern of their uniforms that resembles a beehive honeycomb. Ghosts fashion on a similar pattern, white on grey, on their uniforms under the protective armor.